Apparatus and methods for authentication using partially fluorescent graphic images and OCR characters

ABSTRACT

An authentication system combines a source of ultraviolet light (and optionally a scanning mechanism) with apparatus for capturing and recognizing either graphic images or characters or both, where the graphic images and/or characters have been previously made with fluorescent substances that may be invisible under ordinary visible light, but are rendered detectable by the ultraviolet light. As in conventional optical character recognition (OCR), the characters may be conventional alphanumeric characters readable by human readers once they are made visible. The authentication system has a housing enclosing its optical path, a source of UV light, a detector for detecting graphic images or characters, conversion of the detector signal to digital form, a memory storing predetermined indicia, recognition logic, and indicating means. The system may also include a scanning mechanism and optical filters to select predetermined wavelengths of fluorescent light. The detector may be capable of detecting both fluorescent images and normal visible images, and the authentication system may incorporate switching mechanisms to allow multiplexed acquisition of fluorescent and normally visible images. The authentication system can operate in conjunction with a process for marking articles with indicia selected from a predetermined set of graphic images and characters readable by optical character recognition and/or by image comparison. That process can include printing fluorescent graphic images or characters in registration with (or with predetermined offset from) visible images or characters or indicia printed with substances fluorescent at different wavelengths. The recognition logic of the authentication system can include comparison of fluorescent and visible images or two different fluorescent images with each other. Pairs of indicia to be recognized and/or compared may be arranged to constitute a stereogram or other arrangement for first-order authentication by a human observer.

CROSS-REFERENCE TO RELATED APPLICATIONS

This invention is a continuation-in-part of commonly assignedapplication Ser. No. 09/241,555 by Liang filed Feb. 1, 1999, which wasin turn a division of commonly assigned application Ser. No. 08/863,846by Liang filed May 27,1997, now U.S. Pat. No. 5,867,586, which was inturn a division of commonly assigned patent application Ser. No.08/265,399 by Liang filed Jun. 24, 1994, now U.S. Pat. No. 5,719,948.

This invention is related to a commonly assigned co-pending patentapplication by Liang et al. entitled “Authentication System and Method,”Ser. No. 08/127,250, filed Sep. 27, 1993; and to a commonly assignedco-pending patent application by Liang entitled “Apparatus and Methodfor Calibration of Fluorescence Detectors,” Ser. No. 08/156,249, filedNov. 22, 1993.

FIELD OF THE INVENTION

This invention relates generally to systems for authenticating articles,methods for authenticating articles, and processes for marking articlesfor later authentication. This invention relates particularly tomechanisms and methods for detecting indicia which may include graphicimages and/or characters and for comparing the detected indicia withpredetermined indicia to verify the articles' authenticity if thedetected indicia are recognized. This invention relates moreparticularly to detection, discrimination, and recognition offluorescent indicia rendered detectable by illumination of articles withultraviolet light.

BACKGROUND OF THE INVENTION Problems Solved by the Invention

The counterfeiting of articles of many kinds has become a seriousproblem worldwide, causing great loss of revenues to legitimatebusinesses and to individuals. Counterfeiting has produced articles thatare very difficult to distinguish from the genuine articles, takingsales revenues from the producers of genuine articles and impactinglegitimate business' reputations when the counterfeit articles haveinferior quality and/or non-existent manufacturers' support. Similarly,problems and losses occur due to counterfeiting of articles used forfinancial transactions or identification, such as credit cards, drivers'licenses, passports, and immigration documents. Even when genuinearticles have been marked with authentication markings such aswatermarks, special papers, and holograms which are difficult toreplicate, counterfeiters have managed to produce articles that appeargenuine. The general availability of newer replication technology suchas high-resolution image scanners, laser copiers and printers, andcolor-accurate color copiers and printers has enabled counterfeiters toproduce more credible counterfeit articles. These technologicaldevelopments of replication hardware continue to make rapid progress, asdo the computer hardware and software that support them. Thus it isuseful to have additional ways to mark articles for authentication withgreater security. Greater security may be achieved by makingauthentication markings more difficult for counterfeiters to detect andinterpret, by incorporating greater complexity into the markings, and bymaking replication by counterfeiters more difficult. Combining multiplekinds of marking indicia can further increase the complexity ofdetection, interpretation, and replication, thus providing even bettersecurity. Considering the security issue from another point of view, itis not desirable to use the same means that generated the visibleappearance of an article to authenticate it, as the visible appearanceis becoming easier to replicate. Invisible indicia that cannot bereproduced by common visible graphic copying and printing means canprovide improved security, especially when combined with complex images,patterns, and/or characters.

Notations and Nomenclature

In this specification, the following terms or abbreviations are usedwith the meanings listed here:

CCD—charge coupled device

DSP—digital signal processor

excitation time—a characteristic time for a fluorescent emission to beexcited after ultraviolet illumination of a fluorescent substance begins

extinction time—a characteristic time for a fluorescent emission todecay exponentially from its initial emission intensity I_(O) tointensity I_(O)/e

IR—light in the infrared portion of the spectrum

OCR—optical character recognition

registration—the conventional definition of this term in the fields ofgraphic communication and printing, as defined, for example, in“Glossary of Graphic Communications” compiled by Pamela Groff andpublished by Graphic Arts Technical Foundation (Prentice-Hall, Inc.,Upper Saddle River, N.J., 1998) at pages 245-246.

UV—light in the ultraviolet portion of the spectrum

visible/IR—light either entirely in the visible portion or entirely inthe infrared portion, or partly in both visible and infrared portions ofthe spectrum

visible/UV—light either entirely in the visible portion or entirely inthe ultraviolet portion, or partly in both visible and ultravioletportions of the spectrum

DESCRIPTION OF THE RELATED ART

Many methods have been known to authenticate valuable articles. Someknown methods include imprinting a white-light hologram or imprintingreflective and diffractive indicia which display distinctive images thatare difficult to counterfeit. Other known methods include incorporationof distinctive fibers into the articles, such fibers being detectable byvisual observation, microwave irradiation, or other means. U.S. Pat. No.4,921,280 describes fibers made luminescent by a dyeing processemploying rare-earth compounds, which fibers may be incorporated intoarticles requiring authentication.

It is known that documents may be authenticated by marking the documentswith substances such as inks or dyes that appear invisible or relativelyunnoticeable to the naked eye in ordinary visible illumination, but thatfluoresce when illuminated with ultraviolet light, revealing marks thatserve to identify the legitimate document. These methods depend onsubstances that are not easily or inexpensively identified by acounterfeiter, and not easily or inexpensively duplicated or mimicked bya counterfeiter. When using these methods, it is desirable to usesubstances such as dyes or inks that fluoresce in narrow spectral bandswhich are distinguishable by sufficiently narrow-band detectors, but notreadily distinguishable by eye. In U.S. Pat. No. 4,146,792 by Stenzel etal., these methods are extended to include dyes containing rare-earthelements whose fluorescence is influenced by the chemical environment ofthe fluorescing atoms in a non-fluorescing matrix, and the detection isrefined to include detection of predetermined fine structure in the linespectrum of emitted light. Yet another class of authentication methodsuses substances which fluoresce in the infrared portion of theelectromagnetic spectrum when illuminated by light in the visibleportion of the spectrum.

In U.S. Pat. No. 4,642,526 by Hopkins and assigned to the assignee ofthe present invention, a source of ultraviolet light is madeself-modulating at a predetermined frequency. Detection of the secondaryradiation, filtering of the detected signal, and demodulation of thefiltered signal at the predetermined frequency allow the system ofHopkins' invention to detect the fluorescent marks despite interferencefrom ambient light sources.

Marking products with indicia such as bar codes using fluorescentsubstances such as inks or dyes is also known in the prior art, both forthe purposes described above and for providing identification on theproducts without detracting from the products' appearance as normallyviewed in visible light. U.S. Pat. No. 4,983,817 by Dolash et al.describes methods and apparatus for reading bar codes printed withfluorescent substances, while compensating for variations in backgroundreflectance over the area printed with the bar code. U.S. Pat. No.5,064,221 by Miehe et al. shows the use of fluorescent substances addedto ink ribbon used for printing original documents, in order todistinguish the originals from copies. In many of the knownauthentication methods using fluorescence, the fluorescent identifyingsubstance may be incorporated into the article during the article'smanufacture. In U.S. Pat. No. 4,451,521 by Kaule et al., for example,luminophores are incorporated into paper during its manufacture. Some ofthe fluorescent substances used in the prior art for authenticationpurposes contain heavy metals, which are not as safe or environmentallybenign as substances not containing such heavy metals. While fluorescentsubstances have been used in many ways in the prior art to mark articleswith indicia for interpretation by human observers, to our knowledgeneither optical character recognition (OCR) systems nor imageverification systems have been combined with fluorescent markings and UVlight illumination to provide improved authentication methods.

The technology of automatic pattern recognition is described in a largebody of literature including numerous patents, especially in theapplication area of optical character recognition (OCR). Many of therecent developments in OCR technology (especially in recognition logicsoftware) are usable with the present invention albeit with someadaptation to the type of light source and to such contrast conditionsas may differ from those encountered with conventional OCR scannershaving conventional visible/IR light sources.

OBJECTS AND ADVANTAGES OF THE INVENTION

It is an object of this invention to provide an improved authenticationsystem which can detect and recognize complex authenticating indiciasuch as graphic images and alphanumeric characters. It is another objectof the invention to provide an authentication system which can bereadily automated to provide authentication that does not depend onhuman subjective judgment. It is another object of the invention tocombine the use of substances which fluoresce under UV illumination,detectors capable of detecting fluorescent radiation, and image orcharacter recognition techniques to enable the creation andauthentication of articles with improved security. Another object of theinvention is to enable the use of character or image indicia forauthentication printed with substances that are safer and less likely toharm the environment than substances containing heavy metals. Anotherobject of the invention is to enable the use of character or imageindicia for authentication printed with substances that havesufficiently short extinction times to enable fast scanning. Anotherobject is to enable capture of complex indicia without undue loss ofresolution or smearing of details. Another object is to enable robustidentification of articles of mail using mail bar codes such as“PostNET” codes printed with fluorescent substances. Another object ofthe invention is to enable the use of fluorescent indicia forauthentication that are more complex than bar codes or simple arrays ofdots and/or lines, and that allow a higher density of information perunit area than conventional bar codes. Another object is to provide anauthentication system that makes counterfeiting and fraudulent labelingof articles including documents more difficult and expensive toaccomplish. Another object is to provide a system that can mark articlesfor authentication without unduly compromising their aestheticappearance. Another object is to provide authentication marks that arenot easily removed. Another object is to provide flexible methods ofauthenticating articles that can be practiced in the field of usewithout requiring special printing press equipment. Another object is toprovide an authentication system that can be re-programmed by a user touse various authentication criteria within its range of graphic imageand character recognition capabilities.

SUMMARY OF THE INVENTION

An authentication system in accordance with this invention combines asource of ultraviolet light (and optionally a scanning mechanism) withapparatus for capturing and recognizing either graphic images orcharacters or both, where the graphic images and/or characters have beenpreviously made with fluorescent substances that may be invisible underordinary visible light, but are rendered detectable by the ultravioletlight. As in conventional optical character recognition (OCR), thecharacters may be conventional alphanumeric or other natural-languagecharacters readable by human readers once they are made visible.

The authentication system has a housing enclosing its optical paths, asource of at least UV light, a detector for detecting graphic images orcharacters, conversion of the detector signal to digital form, a memorystoring predetermined indicia, recognition logic, and indicators. Thesystem may also include a scanning mechanism and optical filters toselect predetermined wavelengths of fluorescent light. The detector maybe capable of detecting both fluorescent images and normal visibleimages, and the authentication system may incorporate switchingmechanisms to allow multiplexed acquisition of fluorescent and normallyvisible images produced by visible/IR or visible/UV illumination.

The authentication system can work in conjunction with processesperformed in accordance with this invention, for marking articles withindicia selected from a predetermined set of graphic images andcharacters readable by optical character recognition and/or by imagecomparison. That process can include printing fluorescent graphic imagesor characters in registration (or in predetermined mis-registration)with substantially identically-formed images or characters previouslyprinted with visible substances and/or with fluorescent substances ofdifferent characteristic fluorescent wavelength. The recognition logicof the authentication system can include comparison of these two(fluorescent and visible/IR, fluorescent and visible/UV, or twodifferent fluorescent) images with each other. The process can alsoinclude printing fluorescent graphic images or characters with amultiplicity of fluorescent substances having distinct fluorescentwavelengths and excitation or extinction times, and printing those inoverlay with registration or with predetermined registration offset. Theregistration offset may be selected to produce a predetermined stereoimage when properly viewed by a human observer, thus allowing “firstorder” authentication by visual inspection using suitable filters.Similar first order authentication may be provided by printing graphicimage or character indicia which are both fluorescent and partiallyvisible without UV illumination. Another overlay method uses two graphicimages or character indicia, each incomplete in itself, with unconnectedbut complementary segments. When the two complementary segments arecombined with appropriate registration, a complete recognizable graphicimage, word, or natural language phrase is formed.

Other objects, uses, advantages and features of the invention willbecome apparent to those skilled in the art from the followingdescriptions of preferred embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a functional block diagram of an embodiment of anauthentication system in accordance with the invention.

FIG. 2 is a schematic diagram illustrating an embodiment of theauthentication system.

FIG. 3 is a schematic diagram illustrating another embodiment of theauthentication system.

FIG. 4 is a flow chart illustrating a process for marking articles forauthentication.

FIGS. 5a-5 d are related graphic images illustrating example indiciaused in the authentication system for graphic image recognition.

FIGS. 6a-6 d illustrate example indicia used in the authenticationsystem for optical character recognition (OCR).

FIGS. 7a-7 d illustrate example indicia used in the authenticationsystem for barcode recognition.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The authentication system of the present invention as considered fromone point of view combines as major elements a UV light source 10 forilluminating articles to be authenticated and for excitation offluorescent radiation, a detector 40 for detecting fluorescent radiationfrom indicia on the articles, and recognition logic 70 for recognizingindicia marked on the articles. Recognition logic 70 uses known methodsof character recognition, such as template matching or featureextraction (topological feature analysis), to recognize characters orgraphic images, which may include bar codes. The purposes of theseelements and others and the relationships among them will become clearby reference to the drawings in conjunction with the following moredetailed description.

FIG. 1 shows a functional block diagram of an embodiment of anauthentication system in accordance with the invention. Microcomputer100 controls the overall operation of the authentication system in FIG.1. FIG. 1 is intended to illustrate an overall architecture or systemorganization of such an authentication system. Other embodiments mayvary in some details of their organization, as will be seen from thedescriptions of other embodiments below. For example, in someembodiments, the functions of both recognition logic 70 andmicrocomputer 100 may be performed by a single digital signal processor95 (not shown in FIG. 1, but shown performing various functions in FIGS.2 and 3).

In FIG. 1 a UV source 10 generates ultraviolet light with which toilluminate articles to be tested for authenticity. UV source 10 may be astrobe lamp, and is preferably a high-intensity modulated lamp. Inparticular it may be a self-modulating lamp and associated circuit, asdisclosed in U.S. Pat. No. 4,642,526 by Hopkins, the disclosure of whichis hereby incorporated by reference. Light from UV source 10 passesfirst along an illumination portion 15 of optical path which extends toan article 25 to be authenticated. The light may pass through a beamsplitter 30 and a scanner 60 before impinging on article 25 under test.The apparatus may also include an optional visible/IR source 20 whosepurpose is described below. Beam splitter 30 passes light from either UVsource 10 or both sources 10 and 20 along illumination portion 15 ofoptical path toward the articles, and passes light returned from article25 along a return portion 16 of optical path toward detector 40. Ifarticle 25 has been marked with fluorescent indicia 26, at least some ofthe light returning along return portion 16 of optical path will befluorescent light from indicia 26. Beam splitter 30 may be apartially-reflective mirror or prism or a beam splitter of any type thatcan pass both UV light and the fluorescent light. If visible/IR source20 is used, then beam splitter 30 must also pass visible/IR light.Optical filters 50 may be used in the return portion 16 of the opticalpath to select portions of the spectrum for detection. Filters 50 may bemovable into and out of return portion 16 of optical path. For someapplications it is desirable to insert other optical filters 50 (notshown) into illumination portions 15 of optical path between sources 10and/or 20 and beam splitter 30, to select portions of the UV and/orvisible/IR spectra with which to illuminate article 25. If illuminationportions 15 and return portions 16 of the optical path are separated byother means, or allowed to intermix, beam splitter 30 may be omitted.For applications in which articles 25 to be authenticated aretransported past the authentication system, an integral scanner 60 maynot be needed and may be omitted. Otherwise integral scanner 60 scansthe illuminating beam over the articles or over a selected portion ofeach article containing graphic image or character indicia. Scanner 60may be a set of oscillating mirrors scanning in a two-dimensional rasterfor example. It will be understood by those skilled in the art that, forexample, when article 25 is to be moved past the apparatus, the motionof article 25 may substitute for one direction of scan, and a detector40 consisting of a linear array of sensors oriented perpendicular to themotion may obviate the need for a second direction of scan. If detector40 is a single discrete photodiode, a full two-dimensional scan isneeded to acquire graphic image or character data, or one of thedirections of scan may be replaced with a linear motion of article 25.Thus a wide variety of arrangements is possible with various kinds ofdetectors 40 and with various forms of relative motion between theauthentication apparatus and article 25.

In most applications, speed of authentication is desirable, andtherefore fast detectors 40 and fast scanners 60 (if used) aredesirable. This also has implications for selection of fluorescentmaterials with which to mark indicia 26 on articles 25, to allow forfast scanning without undue loss of resolution or undue smearing of finedetails of image or character indicia 26. The selected fluorescentmaterials preferably have short extinction time (preferably less than 10microseconds). In embodiments having a modulated UV source 10, thefrequency of modulation is preferably selected to take into account theexcitation time of fluorescence of indicia 26. If UV source 10 is astrobe lamp type, the duration and frequency of strobe illumination arepreferably selected to take into account the excitation time.Conventional means such as switches or potentiometers controllingtime-constant circuits (not shown) or program instructions ofmicrocomputer 100 are used for controlling light source modulationfrequency.

Detector 40 may be a photodiode array, a CCD video camera or otherdetector capable of detecting fluorescent light from tested articles atthe desired speed. Preferred detectors are those types that are commonlyused with conventional OCR readers, preferably those that they canefficiently detect the fluorescent light. For example CCD detectors suchas the ICX or ILX Series available from the Sony Corporation may beused. If detector 40 has an analog output signal, then analog-to-digitalconversion circuit 80 is needed to convert that signal to digital form.It will be readily recognized by those skilled in the art that thedigital form may be a binary-coded signal. Of course if detector 40produces a digital output directly, then A-to-D conversion circuit 80 isnot needed. In some embodiments of the authentication system, detector40 may comprise a subsystem with two or more physical detector elements(not shown), each sensitive to a limited spectral range, and connectedto A-to-D conversion circuit 80 (if needed) or to memory 90 through amultiplexer 45. In this type of configuration, outputs of variousdetector elements are multiplexed for input to suitable separate memoryaddresses for comparison with each other and/or with predeterminedgraphic image or character data by recognition logic 70.

A digital representation of the detected fluorescent signal data may bestored in memory 90 for comparison with predetermined image or characterdata previously stored in memory 90 or in a similar memory withinmicrocomputer 100. Microcomputer 100 may be a 68020 microcomputer, forexample, available from Motorola, Inc. along with appropriate supportcircuitry. Microcomputer 100 operates according to program instructionsstored in an internal memory or in memory 90 to control theauthentication apparatus, including recognition logic 70. Whilerecognition logic 70 is shown as a separate entity in the functionalblock diagram of FIG. 1, it will be appreciated that it may beincorporated into microcomputer 100, either as dedicated logic hardwareor as instructions in the stored program of microcomputer 100. Eitherrecognition logic 70 or microcomputer 100 or both can activateindicators 110 to indicate the result of an authentication test.Microcomputer 100 has at least one input/output port 120 through whichpredetermined graphic image or character data may be loaded or changed,and microcomputer 100's program may be loaded and/or changed.Recognition logic 70, which may be implemented by a program ofmicrocomputer 100, uses known methods for comparing characters orgraphic images with predetermined characters or images.

Many methods for comparing a character or graphic image captured bydetector 40 with predetermined characters or images are known, includingmethods such as template matching or feature extraction (topologicalfeature analysis). The images recognized may include bar codes as wellas human-readable natural language characters and simple or complexgraphic images. A simple method of template matching, for example, isdescribed in Dana H. Ballard et al. “Computer Vision” (Prentice-Hall,Inc., Englewood Cliffs, N.J., 1982) Section 3.2.1 (p. 65 ff.). Othermethods of verifying images are discussed in Azriel Rosenfeld et al.“Digital Picture Processing” (Academic Press, New York, N.Y., 1976)particularly in Chapter 10 Section 10.4 and in references cited there(pp. 404-450). More recently developed methods are described in theextensive patent and publication literature of optical characterrecognition and pattern recognition. See for example J. R. Ullman,“Advances in Character Recognition” (pp. 197-236) in K. S. Fu, Ed.“Applications of Pattern Recognition” (CRC Press, Inc., Boca Raton,Fla., 1982) and “Proceedings of 10^(th) International Conference onPattern Recognition” (IEEE Computer Society Press, Los Alamitos, Calif.,1990) Vol. 1 and 2, especially Vol. 1 pages 443-473 and 551-582, andother proceedings of that conference series.

It will be understood that microcomputer 100 may be programmed for itsvarious modes of operation by hardware mode-selection switches (notshown), or by loading appropriate software instructions into its programmemory through input/output port 120. For example, microcomputer 100 maybe programmed to compare two multiplexed images in real time, pixel bypixel, such as a fluorescent image and a visual/IR image, using thesoftware equivalents of a sample and hold circuit and a comparatorcircuit. Alternatively, these functions can be provided in conventionalcircuit hardware. With appropriate timing, and with optical alignment oftwo detectors 40, two multiplexed images may be compared in real time,pixel by pixel, without use of memory 90. The two images may be aconventional image detectable with visible-light illumination and afluorescent image detectable under UV illumination, or two distinctfluorescent images having different fluorescent wavelengths, both madedetectable by UV illumination. Mode-selection switches, mentioned above,may be used to select an image-comparison mode to operate in thismanner. The optical alignment of detectors 40 for image-comparisonoperation may include a predetermined optical axis offset between two ormore detectors. In the simplest embodiment of such a system, the offsetis zero, and two or more images must be printed in registration, i.e.each image printed accurately aligned with the other(s), within apredetermined tolerance. If they are registered within the requiredtolerance, the system produces a positive indication of authenticity,via indicators 110.

Another mode of operation is an offset-image-comparison mode. This modemay be selected by mode-selection switches or under control of a storedprogram of microcomputer 100. A predetermined offset may be switched onor off by a user. Yet another mode of operation selectable by switchesor by stored-program control is a “missing-link” image mode. In thismode of operation, one image contains an incomplete image which ismissing certain elements or segments of a complete image. Thatincomplete image may be a visible image or one made visible only underUV illumination. For a “missing link” mode of operation, at least oneadditional image must be printed which contains the missing segments,filling in a complete image. Only under UV illumination will thecomplete image be detected by detectors 40 and recognized by recognitionlogic 70.

If the two images have opposite contrast (i.e. one has relatively brightindicia on a darker background and the other has dark indicia on abrighter background), then one image is reversed by recognition logic 70before the two images are combined. The two images may then be combinedby a registration operation and an addition operation. For binaryimages, the addition may be a logical non-exclusive OR operation. Bothimages may contain a common element of a convenient design such as across to be used for registration.

Conventional switches may be used in conventional arrangements toactuate movement of optical filters 50 into and out of illuminationportion 15 and/or return portion 16 of the optical path. These filtermovements may be controlled by microcomputer 100 through its storedprogram instructions, instead of or in addition to switches manuallyoperated by a user.

FIG. 2 is a schematic diagram illustrating a first physical embodimentof the authentication system. The system has a housing 200. Housing 200holds and encloses other elements of the system, maintaining opticalalignment, shielding the optical paths from stray light, and protectingthe user from unnecessary exposure to UV light. Housing 200 shouldenclose at least the illumination portion optical path portion 15, UVsource 10 and visible/IR source 20, splitter 30, filters 50 if any, anddetector 40, and may enclose all other elements as well. For someapplications it may be convenient to enclose only the illuminationportion optical path 15, source(s) 10 and/or 20, splitter 30, filters 50if any, and detector 40 in housing 200, and to house the remainingelements of the system separately, connected to the elements in housing200 with a cable or with wireless transmitter and receiver means (notshown) such as radio, ultrasonic or infrared. Of course elements withinhousing 200 and subject to illumination by illumination portion opticalpath 15 or by any scattered UV light should not themselves befluorescent in a spectral range to be detected.

In FIG. 2 UV source 10 is energized by energizing circuit 12, which mayincorporate components making UV source 10 a self-modulating lamp asdiscussed above with reference to FIG. 1. Light propagating alongilluminating optical path portion 15 from source 10 illuminates thearticle 25 to be authenticated, which may carry authenticating indicia26 printed on it in accordance with methods of the invention. Lightreturning along return optical path portion 16 is separated fromilluminating portion by beam splitter 30 or equivalent means. Beamsplitter 30 may be a partially reflective mirror or a suitable prismtransparent to UV light in the direction of illuminating portion opticalpath 15. Return portion optical path 16 is focused by focusing element35 so as to produce an image of article 25 at detector 40. Opticalfilter 50 may be used to select portions of the optical spectrum to bedetected.

Detector 40 is preferably a CCD array detector such as a CCD videocamera. For some applications, however, detector 40 may be a simpler andless expensive linear detector array as discussed above with referenceto FIG. 1. It is important that detector 40 in combination with otherelements of the invention produce sufficient graphic or character datawith sufficient resolution and contrast for optical characterrecognition and/or image comparison by recognition logic 70. In FIG. 2,detector 40 is of a type producing a digital output. Recognition logic70 may be implemented by use of a digital signal processor (DSP) 95, asshown in FIG. 2. In this embodiment digital signal processor 95 performscombined functions of microcomputer 100 and recognition logic 70 of FIG.1, and may also incorporate memory 90. If detector 40 were of a typeproducing analog outputs, DSP 95 could also perform the function ofanalog-to digital conversion 80 shown in FIG. 1. DSP 95 may be aDSP56000, available from Motorola, Inc. for example, along withappropriate support circuitry.

Recognition logic 70 connects to an input/output port 120, through whichthe program under which DSP 95 operates may be loaded. Predeterminedcharacter and/or graphic image data may also be loaded through port 120,and this or other information may be read out. The other information tobe read out may include statistical information gathered by DSP 95 overa period of time, over a number of characters or images tested, or overa number of authenticity determinations made. Recognition logic 70 alsoconnects to indicators 110 and electrical output port 130. Whenrecognition logic 70 has completed a character-recognition operation orimage-comparison operation (or set of such operations) and reached anauthentication result (positive or negative), the authentication resultis displayed on indicators 110 and/or transmitted to electrical outputport 130. Output port 130 may be a relay output, a standard logic outputsuch as TTL, a current loop output, or the like to control otherapparatus outside the authentication system apparatus. Indicators 110may consist of lightemitting diodes, a liquid-crystal display, acathode-ray tube video display or the like to convey an authenticationresult to a human user of the apparatus. In the simple embodiment ofFIG. 2, no scanner 60 is used, and no separate memory 90 is used. Thisembodiment can be used, for example, in an “overlay method,” describedin detail below.

FIG. 3 is a schematic diagram illustrating a second physical embodimentof the authentication system. The embodiment of FIG. 3 combines many ofthe same elements as in the simpler embodiment of FIG. 2 along withadditional elements to provide a more flexible authentication system. Ahousing 200, UV light source 10, energizing circuit 12, beam splitter30, focusing optical element 35, optical filter 50, detector 40,input/output port 120 and electrical output port 130, all of theseperform the same functions as the corresponding elements in FIG. 2. InFIG. 3, microcomputer 100 controls the overall operation of theauthentication system. Control switches 140 allow selection of variousoperating modes by the user. Memory 90 stores predetermined character orgraphic image data, and image data acquired by detector 40, undercontrol of microcomputer 100. The function of recognition logic 70 isperformed by the combination of microcomputer 100 and DSP 95. Operatingparameters of several elements are controlled by microcomputer 100. Amodulation frequency of UV source 10, for example may be controlled bymicrocomputer 100 by varying the frequency of trigger pulses or byswitching various capacitors into a resonant circuit including the lampof UV source 10. The axial position of focusing optical element 35 maybe controlled by actuating a stepper motor with pulses frommicrocomputer 100. The positions of filters 50 may be similarlycontrolled to move filters 50 into or out of an optical path. Theoperation of detector 40 may be controlled by microcomputer 100,including synchronizing an image acquisition operation with theoperation of UV source 10. Scanner 60 scans article 25 for thoseapplications that require scanning, and its frequencies and amplitudesof scanning may be controlled by microcomputer 100. In the embodiment ofFIG. 3, indicator 110 may display a processed image and/or a raw,unprocessed image of article 25 or indicia 26.

It will be understood that microcomputer 100 may be programmed for itsvarious modes of operation by hardware control switches 140 selectingthe various modes, or by loading appropriate software instructions intoits program memory through input/output port 120.

FIG. 4 is a flow chart illustrating a process for marking articles forauthentication in accordance with the invention. First (S1), a suitablecarrier medium and predetermined fluorescent substances are provided.The carrier medium may be a non-fluorescent transparent solvent orliquid plastic. The fluorescent substances are preferably substanceswhich fluoresce in the blue portion of the optical spectrum at about 465nanometers wavelength, substances which fluoresce in the green portionof the optical spectrum at about 510 nanometers wavelength, substanceswhich fluoresce in the yellow portion of the optical spectrum at about530 nanometers wavelength, and mixtures of those substances, which maybe easily distinguished using readily available optical filters.Fluorescent substances are preferred which fluoresce in the portions ofthe optical spectrum between 455 and 475 nanometers wavelength, between500 and 520 nanometers wavelength, between 520 and 540 nanometerswavelength, and between 580 and 630 nanometers wavelength, and theirmixtures (in the same indicia) or combinations (in different indicia).Suitable substances are Angstrom No. 5, Angstrom No. 4, and Angstrom No.6, available from Angstrom Technologies, Inc., which fluoresce in thefirst three above-mentioned spectral ranges respectively, and pentacene(C₂₂H₁₄) which fluoresces in the fourth above-mentioned spectral range.Fluorescent substances to be used in the methods of this invention mayinclude substances and chemical compositions as described in U.S. Pat.No. 4,642,526 by Hopkins, the disclosure of which is hereby incorporatedby reference. It is especially preferred to provide fluorescentsubstances without heavy metals (i.e. having metals, if any, with atomicnumbers less than or equal to 20). These are safer and less likely toharm the environment than substances containing heavy metals. It is alsoespecially preferred to provide substances that have sufficiently shortextinction times to enable fast scanning for capture of complex indiciawithout undue loss of resolution or smearing of details.

The fluorescent substances are mixed (step S2) with the carrier mediumin predetermined concentrations. Preferred concentrations are less than10% by weight, and even more preferred, less than 1% by weight.

In step S3, indicia are selected from predetermined sets of charactersor graphic images suitable for recognition. The predetermined characterspreferably include a font of characters standardized for opticalcharacter recognition. Examples of such standardized character sets areOCR-A, OCR-B, E-13B, OCR-A Eurobanking and OCR-B Eurobanking. For mailsorting or authentication, standardized postal bar code indicia such asthe “PostNET” code are preferred. Preferred indicia for otherauthentication applications are more complex than bar codes or simplearrays of dots and/or lines. However, it should be noted that themethods of this invention are not limited to Roman alphabet fonts orfonts especially designed for OCR, but may be used with a wide varietyof character indicia, including characters of foreign languages such asCyrillic, Chinese, Japanese, Hebrew and Arabic language characters, andan even wider variety of arbitrarily designed graphic images.

At this point in the process, a series of decisions are made whichdetermine whether indicia to be printed will be aligned with previouslyprinted marks. The first decision (step S4) is whether an overlay methodwill be used. If not, the selected indicia are printed without alignment(step S9). If an overlay method is to be used, the decision made in stepS5 determines if it is to be registered overlay. If so, the selectedindicia are aligned in registration with previously printed indicia(step S7), and then printed (S9). If the method is to be an offsetoverlay (decided in step S6), then the selected indicia are aligned witha predetermined offset (S8), and then printed (S9). Many methods ofalignment or registration of printed indicia are known in the art,including the methods used to register the various color levels in coloroffset printing.

The methods of the invention as illustrated by the method of FIG. 4 maybe used on a variety of articles, including articles made of paper,synthetic paper, tamper-resistant paper, cardboard, fabric, plasticfilm, ceramic, metal and glass.

The invention will be further clarified by considering the followingexamples, which are intended to be purely exemplary of various ways touse the invention.

The authentication system is easy to use and flexible in its uses. In afirst phase of using the invention, the articles to be authenticated aremarked by a process in accordance with the flow diagram of FIG. 4. Theimages may be graphic representations of a company's logo, for example.Or the indicia may be a series of English alphanumeric characters codingsome unique characteristics of the article being marked. In a secondphase of using the authentication system, a determination is madewhether particular articles have been so marked.

In one method of using the authentication system, the graphic imagesand/or characters to be recognized are stored in memory 90 usinginput/output port 120. Articles to be tested for authenticity are movedpast the optical input of the authentication system if it is of a typenot having an integral scanner 60. If the authentication system doeshave an integral scanner 60, relative motion of the system and thearticles is not needed (nor is relative motion desirable). In eithercase, UV source 10 illuminates the articles, and detector 40 captures aninstantaneous image. Recognition logic 70 will automatically indicateauthentication only if the detected graphic image or characters matchthe stored image data to within predetermined criteria and theirtolerances.

In another method of using the authentication system (here termed“overlay method”), there are again two phases. In the first phase,indicia selected from a predetermined set of images or charactersrecognizable by the authentication system are printed on articles withordinary visible ink. These indicia may represent a serial number, forexample. The same images or characters are printed on the same articleswith fluorescent ink prepared as described above. Preferably the secondprinting is printed over the first (visible) printing in registrationwith the visible printing. Thus it would not be apparent that thearticle carried additional non-visible markings. Useful alternativesinclude printing indicia with ink fluorescent in one preselectedwavelength over identical indicia fluorescent in a different preselectedwavelength, or printing first fluorescent indicia over either visible orsecond fluorescent indicia with a predetermined registration offset—i.e.shifted by a predetermined distance and direction from the firstprinting. The latter may be called an “offset overlay method.” In afurther application of the offset overlay method, the overlay offset andthe two overlaid images may be selected to produce a predeterminedstereo three-dimensional image when viewed from normal near-pointreading distance (25 cm.) by a human observer through suitable filtersdiffering for the observer's two eyes. This application (“stereo offsetoverlay”) allows a human observer to accomplish a “first-order”authentication—i.e. an authentication with less precision and certaintythan that performed by methods using the apparatus of this invention.First-order authentication may be conveniently used at a point-of-sale,immigration or customs checkpoint, etc. for a rapid informal check on anarticle's authenticity. As there is some variation among observers withrespect to inter-ocular spacing, and in their ability to easilyassimilate variously spaced stereo pairs of images presented separatelyto their eyes, there is a range of offsets that providesthree-dimensional appearance, which will vary somewhat in apparent depthdepending on the observer. The stereo pair of images may be of the typecommonly called “random dot stereograms,” in which no structure isevident to the human eye until the stereogram images are fused toproduce a three-dimensional effect.

This completes the first phase of using the system in the overlaymethod. The second phase of the overlay method is using theauthentication system to determine if the indicia are authentic. Forthis second phase, the authentication system is switched to “overlaydetection” mode. In this mode the authentication system scans thearticle first with visible/IR light and (after conversion to digitalform) stores the visible/IR image data. It then scans the same articlewith UV light and stores the (digitally converted) fluorescent imagedata. These two scanning, detection, conversion and storage sequencescan be quasi-simultaneous operations by using the multiplexing optiondescribed above. The recognition logic compares the digital data storedfrom visible/IR and fluorescent image scans (performing a softwareregistration if necessary), and indicates a positive authenticationresult if and only if the two images agree within the programmedtolerance. If the images have been intentionally printed with apredetermined offset (offset overlay method), then the recognition logicis programmed to test for the predetermined registration offset (towithin a predetermined tolerance) as well as for correspondence of theindicia. This offset testing may be done, for example, by firstutilizing known methods of registering similar images (such asmaximizing a cross-correlation coefficient). Then the offset distanceand direction required to achieve best registration is determined. Thetest is completed by comparing that offset with the predeterminedoffset. The same method may be used for automatic testing of stereooffset overlay images. Other stereo image interpretation methods mayalso be used (such as those discussed in W. Luo and H. Maitre at pages60-64 in Vol. 1 of “Proceedings 10th International Conference on PatternRecognition” cited above, and in other papers in those proceedings andthose of other conferences in that series).

In a variation of the overlay methods described above (here termed“missing link overlay”), the two overlaid images may comprise acomplementary pair in which detailed elements of one member of the paircomplete a recognizable image by filling in detail elements missing fromthe other member of the pair. One member of the pair is again printedwith visible ink or a first fluorescent ink, and the other member of thepair is printed in a fluorescent or a second fluorescent inkrespectively. For example indicia in one member of the pair may compriseportions of characters of a complete English word or phrase, and theother indicia may comprise the remaining portions of those characters,such that either image alone is not readily recognizable by a humanobserver or by a conventional OCR system, but when the two indicia arecombined by the system of this invention, the complete word or phrasemay be recognized. A simple example of non-character missing-link imagesis a pair of images, each containing different portions of a completerecognizable object, such as a bicycle. Thus the missing link overlaymethod also allows first-order authentication by a human observer.

It will be noted that some of the methods of using the invention mayrequire (as part of the automatic image acquisition process orrecognition process), contrast reversal of an image or of one image of apair, while not requiring contrast reversal of the other image of apair. Thus for example, while indicia printed with visible ink may berecognized by conventional OCR apparatus, other indicia printed withfluorescent ink may have bright indicia against a darker background, andthus may require contrast reversal before recognition by similarrecognition logic. With digital representation of the detected indicia,any required contrast reversal is easily incorporated into the programof microcomputer 100 or DSP 95.

As mentioned above, the system can be used in a “missing-link” mode ofoperation in which the graphic image(s) and/or OCR-recognizablecharacters are formed by combining first portions visible under visiblelight illumination with second portions visible only under non-visibleillumination, e.g. by virtue of fluorescence of the second portions. Inthis missing-link method, the entire graphic image or the entireOCR-readable text is not apparent to a human observer or recognizable bya human observer under ordinary ambient visible-light lightingconditions.

The operation of the authentication system in its “missing-link” mode ofoperation is now illustrated by the examples shown in FIGS. 5a-5 d andFIGS. 6a-6 d. FIGS. 5a-5 d show examples of indicia used in theauthentication system for graphic image recognition in the“missing-link” mode of operation. It will be seen that none of theindicia of FIGS. 5a, 5 b, and 5 d is individually recognizable by ahuman observer, while the combination in FIG. 5c is readily recognizableby a human observer as the Statue of Liberty. The indicia of FIG. 5aconsist of selected fragments of the indicia of FIG. 5c. The fragmentsin FIG. 5a may together comprise any desired fraction of the image areaof the indicia of FIG. 5c, for example, but these fragments arepreferably selected to be approximately half of the image area of FIG.5c. The fragments in FIG. 5a may be selected by a random orpseudo-random process so as to avoid being readily predictable by acounterfeiter. In use of the invention, the indicia of FIG. 5a areprinted with ink visible under illumination with visible light. Thus,under illumination with visible light alone, only the unrecognizableindicia of FIG. 5a are seen by a human observer. Indicia correspondingto either FIG. 5b or FIG. 5d are printed with ink visible only underillumination with non-visible light, e.g. fluorescent ink. Someespecially suitable fluorescent substances visible only under UVillumination, for example, are the Angstrom SC254, SC25, and SC138fluorescent materials, commercially available from AngstromTechnologies, Inc. of Erlanger, Ky. Other suitable substances aredescribed in U.S. Pat. No. 5,714,291 to Marinello et al., the entiredisclosure of which is incorporated herein by reference. Conventionalfluorescent inks visible only under UV may be used for someapplications. The selection of indicia of FIG. 5b or FIG. 5d isdetermined by relative contrast considerations and/or by a tradeoff withcomplexity of the authentication system, as explained below. Forunderstanding of the missing-link method, it is sufficient at this pointto consider the indicia of FIG. 5b and their relationships with those ofFIG. 5a. The indicia of FIG. 5b are printed with ink visible only underillumination with non-visible light, e.g. with fluorescent ink, and areprinted in registration with the indicia of FIG. 5a, i.e., aligned withthe indicia of FIG. 5a to within a predetermined precision. Like theindicia of FIG. 5a, the indicia of FIG. 5b consist of selected fragmentsof the indicia of FIG. 5c, but those fragments in the indicia of FIG. 5bare generally the fragments missing from the indicia of FIG. 5a. Thus,the indicia of FIG. 5b provide the missing link (missing from thevisible indicia of FIG. 5a) needed to form the complete indicia of FIG.5c.

As in FIG. 5a, the fragments in the indicia of FIG. 5b taken togethermay also comprise any desired fraction of the image area of the indiciaof FIG. 5c that is at least the complement of the fractional portionrepresented by FIG. 5a, but are also preferably selected to beapproximately half of the image area of the indicia of FIG. 5c. It willbe understood that the fragments in the indicia of FIG. 5b may not beselected by a random process entirely independently from the selectionin FIG. 5a. However, there may be some overlap in the two portions ifdesired, and that overlap portion may be selected by a random orpseudo-random process so as to avoid being readily predictable by acounterfeiter.

FIG. 5d illustrates an alternative to FIG. 5b, taking into account therelative contrast of the inks used and the common background. In somesituations it may be necessary to use an image like that of FIG. 5dinstead of one like FIG. 5b, because in use, the indicia of FIG. 5a areprinted with ink darker than the background, while the ink visible onlyunder illumination with non-visible light, e.g. fluorescent ink, isbrighter than the same common background. The indicia of FIG. 5d differfrom the indicia of FIG. 5b essentially in having reversed contrast.Such reversed contrast printing is not necessary, however if humanrecognition of the completed image such as the indicia of FIG. 5c is notrequired, as the logic of the authentication system hardware or softwarecan include a logical inversion of the contrast obtained withillumination with non-visible light. Such inversion adds some complexityand cost to the authentication system hardware or software, whichcomplexity and cost may be avoided by the use of indicia such as theindicia shown in FIG. 5d.

The missing-link mode of operation has been described above in terms ofcombining first portions visible under visible light illumination withsecond portions visible only under non-visible illumination. The sameprinciples are also applicable in situations that benefit from havingboth portions visible only under non-visible illumination. For example,referring again to FIGS. 5a-5 d, FIG. 5a may be printed in ink visible(having a first fluorescent color) only under invisible ultraviolet (LW)illumination characterized by certain first wavelengths of ultravioletlight and FIG. 5b printed in ink visible only under invisible infrared(IR) illumination. The portions visible under UV may be inks containingthe materials mentioned above, available from Angstrom Technologies,Inc. of Erlanger, Ky., for example. The portions visible only under IRillumination may be printed in inks such as SICPA Securink infrared ink171075A, optionally used with ink 171055A, both commercially availablefrom SICPA Management S.A. of Prilly, Switzerland (SICPA Securink ofSpringfield, Va. in the United States). Similar inks are available inwet- or dry-offset and screen-printing versions. Or, alternatively, FIG.5b may be printed in ink visible with ink having a second fluorescentcolor under illumination by the invisible ultraviolet illumination ofthe same first wavelengths of ultraviolet light that reveal the indiciaof FIG. 5a. Yet another combination uses two substances that requiredifferent wavelengths of UV light, e.g. one ink visible inlong-wavelength UV and one ink visible in short-wavelength UV. Bothwavelengths of UV illumination are then provided to complete the image.In each of these alternative methods, the complete indicia of FIG. 5care visible only when the appropriate combination of invisibleilluminations is provided. Thus, important variables available to becontrolled for implementing the missing-link method of the presentinvention are the wavelengths of invisible illumination employed(combined either with each other or with visible illumination) and theresponses of inks (e.g., their fluorescence, reflectance, transparency,or contrast) in response to illumination with the various wavelengths.Other variables may also be controlled, such as the background color,fluorescence of the background, optical filtering of the illumination,or optical filtering in the optical path used for detecting the indicia.Thus, the missing-link method of the present invention may be practicedwith any combination of multiple portions printed in registration witheach other, of which one or more portions are printed with a substancevisible only under non-visible illumination so that the completecombination of portions (fitting together to form a single completeimage or OCR-recognizable text) is recognizable only when suitableillumination is applied. The one or more portions that are printed witha substance visible only under non-visible illumination may be thoughtof as the link(s) that are “missing” in the missing-link method sincethey are not detectable under ordinary visible illumination.

For simplicity and clarity of exposition, the following descriptionreturns to the combination previously described, viz., first indiciaportions visible under visible light illumination combining with secondindicia portions visible only under non-visible illumination.

It will be recognized that the missing-link mode of operation requiresthat the indicia printed in ink visible under ordinary visible-lightillumination (e.g. the indicia of FIG. 5a) and the indicia printed inink visible only under illumination by non-visible light (e.g. theindicia of FIG. 5b) must be properly registered with respect to eachother on the article in order to form the indicia of FIG. 5c by theirsuperposition. Here, of course, “registration” refers to alignment ofthe indicia so that corresponding points are coincident. Suchregistration requires positioning the respective images in their “x andy” locations on the article to within a predetermined tolerance. Thattolerance will typically be the maximum error in lateral alignment ofthe indicia relative to each other. The registration of printed indiciaand various methods for achieving proper registration are well known inthe printing arts, especially in the field of conventional half-tonecolor printing where three or four separate color component indicia mustoften be printed in precise registration.

It should also be recognized that fluorescence, while sufficient in manyinstances for an image portion to be visible only under non-visibleillumination, is not a necessary characteristic of a substance used toprint such an image portion. Another characteristic useful in thisregard is the contrast of a substance with a background. THUS, FIG. 5amay be printed with ordinary ink on a suitable background against whichit is visible under ordinary visible illumination. FIG. 5b may beprinted with a different ink on the same background, against which it isnot visible under ordinary visible illumination because of insufficientcontrast (e.g., due to relative reflectance, transparency, or colorcontrast). In accordance with the present invention, FIG. 5b may beprinted to be visible under ultraviolet (UV) or infrared (IR)illumination because of the contrast of its ink with the backgroundunder either or both of those non-visible illuminations. FIG. 5a remainsvisible in this example, either because it is also visible under thenon-visible illumination, or there is sufficient visible illuminationpresent in the ambient environment, or applied by suitable apparatus.The same considerations regarding relative contrast apply in thissituation, analogously to the discussion of FIG. 5d above. Again, evenwithout fluorescence, the recognizable combination FIG. 5c becomesrecognizable with suitable illumination that completes the “missinglink.”

FIGS. 6a-6 d show examples of indicia used in the authentication systemin the “missing-link” mode of operation for optical characterrecognition (OCR). The indicia of FIGS. 6a-6 d are analogous to thecorresponding FIGS. 5a-5 d, except that the completed indicia of FIG. 6cform OCR-recognizable text characters. In one sense, this may be thoughtof as a special case of the missing-link mode using graphic images, asthe indicia of FIGS. 6a-6 d may be considered graphic images, and thecompleted indicia of FIG. 6c may be considered a particular kind ofgraphic image that depict text. It will be seen that none of the indiciaof FIGS. 6a, 6 b, and 6 d is individually recognizable by a humanobserver, while the completed combination in the indicia of FIG. 6c isreadily recognizable by a human observer as the text “Ångstrom.” Thetext “Ångstrom” revealed in the combination shown in the indicia of FIG.6c is also OCR-recognizable.

The following description of FIGS. 6a-6 d is thus entirely analogous tothe description above of FIGS. 5a-5 d. The indicia of FIG. 6a consist ofselected fragments of the indicia of FIG. 6c. The fragments in FIG. 6amay together comprise any desired fraction of the total area of theindicia of FIG. 6c, for example, but these fragments are preferablyselected to be approximately half of the indicia area of FIG. 6c. Thefragments in FIG. 6a may be selected by a random or pseudo-randomprocess so as to avoid being readily predictable by a counterfeiter. Inuse of the invention, the indicia of FIG. 6a are printed with inkvisible under illumination with visible light. Thus, under illuminationwith visible light alone, only the unrecognizable indicia of FIG. 6a areseen by a human observer. Indicia corresponding to either FIG. 6b orFIG. 6d are printed with ink visible only under illumination withnon-visible light, e.g. fluorescent ink. The selection of indicia ofFIG. 6b or FIG. 6d is again determined by relative contrastconsiderations and/or by a tradeoff with complexity of theauthentication system, as explained above. For understanding of themissing-link method, it is sufficient at this point to consider theindicia of FIG. 6b and their relationships with those of FIG. 6a. Theindicia of FIG. 6b are printed with ink visible only under illuminationwith non-visible light, e.g. with fluorescent ink, and are printed inregistration with the indicia of FIG. 6a, i.e. aligned with the indiciaof FIG. 6a to within a predetermined precision. Like the indicia of FIG.6a, the indicia of FIG. 6b consist of selected fragments of the indiciaof FIG. 6c, but those fragments in the indicia of FIG. 6b are generallythe fragments missing from the indicia of FIG. 6a. Thus, the indicia ofFIG. 6b provide the missing link (missing from the visible indicia ofFIG. 6a) needed to form the complete recognizable indicia of FIG. 6c.

As in FIG. 6a, the fragments in the indicia of FIG. 6b taken togethermay also comprise any desired fraction of the image area of the indiciaof FIG. 6c that is at least the complement of the fractional portionrepresented by FIG. 6a, but the fragments are also preferably selectedto be approximately half of the indicia area of the indicia of FIG. 6c.Again, as in the case of FIGS. 5a-5 d, there may be some overlap in thetwo portions if desired, and that overlap portion may be selected by arandom or pseudo-random process so as to avoid being readily predictableby a counterfeiter.

FIG. 6d illustrates an alternative to FIG. 6b, taking into account therelative contrast of the inks used and the common background. In somesituations it may be necessary to use indicia like the indicia of FIG.6d instead of indicia like those of FIG. 6b, because in use, the indiciaof FIG. 6a are printed with ink darker than the background, while theink visible only under illumination with non-visible light, e.g.fluorescent ink, is brighter than the same common background. Theindicia of FIG. 6d differ from the indicia of FIG. 6b essentially inhaving reversed contrast. Such reversed-contrast printing is notnecessary, however if human recognition of the completed image such asthe indicia of FIG. 6c is not required, as the logic of theauthentication system hardware or software can include a logicalinversion of the contrast obtained with illumination with non-visiblelight, as discussed above with respect to FIGS. 5a-5 d.

FIGS. 7a-7 d illustrate example indicia used in the authenticationsystem for barcode recognition in accordance with the present invention.Generally, the descriptions above of the relationships among FIGS. 5a-5d and among FIGS. 6a-6 d apply analogously to FIGS. 7a-7 d. Thus, FIG.7c is a complete and valid barcode that is recognizable by imagecomparison or by OCR. FIG. 7d is the negative of FIG. 7b, presented asan alternative to FIG. 7b, for taking into account the relative contrastof the inks used and the common background. However, FIGS. 7a-7 d alsoillustrate a further useful feature of the invention. One way ofdescribing this feature is by noting that the separation into twoincomplete images has been made only along one dimension, perpendicularto the bars. In other words, each bar of FIGS. 7a and 7 b is a selectedportion of a selected bar of FIG. 7c, formed by dividing the selectedbarcode bars lengthwise. Each of FIGS. 7a, 7 b, and 7 d has the generalappearance of a barcode, but the indicia of these three figures are notvalid barcodes. Scanning of any of FIGS. 7a, 7 b, or 7 d with aconventional barcode scanner would fail to produce a valid scan (i.e.,readout of a valid code). Only FIG. 7c, which consists of a combinationof FIGS. 7a and 7 b by registered superposition of the two, is acomplete, valid barcode, which in fact, decodes as the word “Angstrom.”

The printing of image or character portions may be done by using a colorprinter such as a color laser printer or color inkjet printer.(Monochrome or “black-and-white” types of printers may be used withmultiple passes for the various inks, with some added inconvenience.)The image or character portions that are to be visible under non-visibleillumination are printed with toner (in the case of a color laserprinter) or inkjet ink (in the case of an inkjet printer) containingsuitable substances such as fluorescent substances described above. Suchmethods are described in the U.S. Pat No. 5,714,291 to Marinello et al.,mentioned above and incorporated herein by reference.

It will be recognized that the novel “missing-link” method of thepresent invention may be applied to any of the standard barcodesymbologies, including linear codes (e.g., UPC-A, UCC/EAN-14, orUCC/EAN-128) or two-dimensional symbologies (e.g., those known asPDF417, Data Matrix, MaxiCode, or QR Code), or to composite barcodes(e.g., RSS-14 Stacked or RSS-14 Limited), or to any other barcodesymbologies that may be developed in the future. As is known in the art,various barcode symbologies, when valid, can be recognized by imagecomparison, by OCR methods, or by other techniques.

Of course, the completed characters in the indicia formed by thecombination of incomplete indicia can spell messages, such assecurity-related messages that are more extensive than a single word. Anexample of such a security-related message is “A genuine article willshow this message and an image of the Statue of Liberty.” Thus, themissing-link mode of operation may include the use of either graphicimages or OCR-recognizable text or some combination of graphic imagesand OCR-recognizable text. For some applications using a combination ofgraphic images and text, it is preferable that the text and graphicimage be related to each other. For example, the text may explicitlyrefer to a graphic image, as in the security message example above. Inaddition, a graphic image formed using the missing-link mode ofoperation may be used to point to the text, surround the text, orotherwise call attention to the text for the benefit of the user.

While the examples of images and OCR-recognizable characters shown inthe drawings and described in the accompanying descriptions are binary(nominally “black and white,” encoded with two bits) for simplicity andclarity of the description, those skilled in the art will recognize thateither the images or OCR characters and both the visible and fluorescentsub-portions of each may be gray-scale images encoded with more than twobits.

Either the visible sub-image or the fluorescent sub-image or thecombination image may further contain steganographic or so-called“digital watermark” information encoded and inserted in accordance withany of several methods known in the art (e.g., methods as disclosed inU.S. Pat. Nos. 5,710,834; 5,745,569; 5,745,604; 5,748,763; 5,748,783;5,768,426; 5,822,432; 5,822,436; 5,832,119; 5,841,886; 5,841,978;5,850,481; 5,862,260; and 5,889,868, the entire disclosure of each ofwhich is inserted herein by reference). Those skilled in the art willrecognize that the steganographic or digital watermark information maysimilarly be encoded and inserted into the visible and/or fluorescentsub-portions and/or the recombined OCR characters such as those of FIGS.6a-6 d.

Other embodiments of the invention will be apparent to those skilled inthe art from a consideration of this specification or from practice ofthe invention disclosed herein. For example, while FIGS. 1, 2 and 3 showa beam splitter 30 separating illuminating optical path portion 15 fromreturn optical path portion 16, these portions may be separated insteadby an opaque wall or septum which may be an integral part of housing200, or one or both optical path portions may be confined to separateoptical fibers. If it is required to bend illuminating optical pathportion 15 and/or return optical path portion 16, that optical path maybe bent by other conventional means such as mirrors, prisms, opticalfibers, or light pipes. Various optical components shown in the drawingsmay be rearranged while still performing substantially the samefunctions. For example focusing optical element 35 may be a mirror orholographic optical element instead of the conventional lens illustratedin FIG. 2. Also, optical element 35 may be re-positioned to operate onboth illuminating portion 15 and return portion 16 of the optical path.

While uses of the authentication system and methods have been describedin terms of authentication, it will be clear that the same apparatus andmethods may be useful for applications other than authentication, suchas mail sorting, quality control of articles during their manufacture,or identification of articles during shipping, repair, or cleaning, etc.It is intended that the specification and examples be considered asexemplary only, with the true scope and spirit of the invention beingdefined by the following claims.

Having described my invention, I claim:
 1. A method of authenticatingarticles, comprising the steps of: a) selecting a set of indiciarecognizable by automatic optical character recognition; b) providingarticles of which authentic instances are known to have been identifiedwith said selected indicia such that each of said selected indiciacomprises two portions in complementary pair relationship, neither ofsaid two portions by itself forming a complete recognizable character:(i) a first portion comprising first detail elements that emitfluorescent light in predetermined portions of the optical spectrum whenilluminated by light outside of the visible spectrum, and (ii) a secondportion comprising second detail elements complementary to said firstdetail elements, said first and second portions being overlaid relativeto each other so as to complete said selected indicia; c) illuminatingsaid articles with said light outside of the visible spectrum whileselecting said predetermined portions of the optical spectrum and whileperforming said automatic optical character recognition; and d)providing an affirmative output if and only if said indicia arerecognized, thereby confirming the authenticity of those instances ofsaid articles so identified.
 2. The method of claim 1, furthercomprising the step of: e) before said article-providing step (b),identifying said articles by marking with said selected indicia suchthat said first detail elements of said first portion are made withfluorescent ink, while said second detail elements of said secondportion of said selected indicia are made with a visible ink.
 3. Themethod of claim 1, wherein said light outside of the visible spectrumcomprises ultraviolet light.
 4. The method of claim 1, wherein saidlight outside of the visible spectrum comprises infrared light.
 5. Amethod of authenticating articles, comprising the steps of: a) selectinga set of graphic image indicia recognizable by automatic image matching;b) providing articles of which authentic instances are known to havebeen identified with said selected graphic image indicia such that eachof said selected graphic image indicia comprises two portions incomplementary pair relationship, neither of said two portions by itselfforming a complete recognizable image: (i) a first portion comprisingfirst detail elements that emit fluorescent light in predeterminedportions of the optical spectrum when illuminated by light outside ofthe visible spectrum, and (ii) a second portion comprising second detailelements complementary to said first detail elements, said first andsecond portions being overlaid relative to each other so as to completesaid selected graphic image indicia; c) illuminating said articles withsaid light outside of the visible spectrum while selecting saidpredetermined portions of the optical spectrum and while performing saidautomatic image matching; and d) providing an affirmative output if andonly if said graphic image indicia are recognized, thereby confirmingthe authenticity of those instances of said articles so identified. 6.The method of claim 5, further comprising the step of: e) before saidarticle-providing step (b), identifying said articles by marking withsaid selected graphic image indicia such that said first detail elementsof said first portion are made with fluorescent ink, while said seconddetail elements of said second portion of said selected graphic imageindicia are made with a visible ink.
 7. An authenticatable document foridentification or for use in financial transactions, comprising: a) asubstrate suitable for printing with fluorescent ink, and b) selectedindicia, selected portions of said selected indicia being printed onsaid document with fluorescent ink containing predeterminedconcentrations of one or more fluorescent substances, both said selectedindicia and said fluorescent substances encoding predeterminedcharacteristics of said authenticatable document, said selected indiciabeing selected from predetermined sets of: (i) characters readable byautomatic optical character recognition only when said selected portionsof said selected indicia are illuminated with ultraviolet light, and(ii) graphic images recognizable by automatic image comparison only whensaid selected portions of said selected indicia are illuminated withultraviolet light, said selected indicia being further characterized inthat each of said selected indicia comprises two portions incomplementary pair relationship, neither of said two portions by itselfforming a complete recognizable character or image: (A) a first portioncomprising first detail elements that emit fluorescent light inpredetermined portions of the optical spectrum when illuminated withsaid ultraviolet light, and (B) a second portion comprising seconddetail elements complementary to said first detail elements, said firstand second portions being overlaid relative to each other so as tocomplete said selected indicia.
 8. An authenticatable document as inclaim 7, wherein said substrate is a material selected from the listconsisting of paper, cardboard, fabric, plastic, ceramic, metal, andglass.
 9. An authenticatable document as in claim 8, wherein said paperis selected from the list consisting of rag paper, linen paper, mixedpulp and rag paper, recycled paper, vellum, synthetic paper, currencypaper, security paper, and tamper-resistant paper.
 10. Anauthenticatable document as in claim 7, wherein said substrate is aplastic card.
 11. An authenticatable document as in claim 7, whereinsaid selected indicia are printed in registration with selected secondindicia printed on said substrate.
 12. An authenticatable document as inclaim 11, wherein said selected indicia are printed in registration withselected second indicia, said second indicia being indentical indiciaprinted on said substrate with ink visible under illumination within thevisible spectrum.
 13. An authenticatable document as in claim 7, whereinsaid selected indicia are printed in predetermined offset fromregistration with images or characters printed with visible substances.14. An authenticatable document as in claim 7, wherein said ink visibleonly under illumination with light outside of the visible spectrumcomprises predetermined concentrations of one or more fluorescentsubstances, and said selected indicia are printed in predeterminedoffset from registration with images or characters printed withfluorescent substances of different characteristic fluorescentwavelength from said selected indicia.
 15. An authenticatable documentas in claim 13, wherein said selected indicia and said images orcharacters previously printed each forms an incomplete image, and theircombination forms a single image recognizable by said automatic imagecomparison.
 16. An authenicatable document as in claim 15, wherein saidselected indicia comprise barcodes.
 17. An authenticatable document asin claim 16, wherein said selected portions of said selected indicia areformed by dividing individual bars of said barcodes lengthwise.
 18. Anauthenticatable document as in claim 14, wherein said selected indiciaand said images or characters previously printed with fluorescentsubstances of different characteristic fluorescent wavelength from saidselected indicia each forms an incomplete image, and their combinationforms a single image recognizable by said automatic image comparison.19. An authenticatable document as in claim 18, wherein said selectedindicia comprise barcodes.
 20. An authenticatable document as in claim19, wherein said selected portions of said selected indicia are formedby dividing individual bars of said barcodes lengthwise.
 21. Anauthenticatable document as in claim 7, wherein said selected indiciainclude steganographically encoded information.
 22. An authenticatabledocument as in claim 7, wherein said images or characters includesteganographically encoded information.
 23. An authenticatable documentfor identification or for use in financial transactions, comprising: a)a substrate suitable for printing with fluorescent ink, and b) selectedindicia, selected portions of said selected indicia being printed onsaid document with fluorescent ink containing predeterminedconcentrations of one or more fluorescent substances, both said selectedindicia and said fluorescent substances encoding predeterminedcharacteristics of said authenticatable document, said selected indiciabeing selected from predetermined sets of characters readable byautomatic optical character recognition only when said selected portionsof said selected indicia are illuminated with ultraviolet light saidselected indicia being further characterized in that each of saidselected indicia comprises two portions in complementary pairrelationship, neither of said two portions by itself forming a completerecognizable character: (A) a first portion comprising first detailelements that emit fluorescent light in predetermined portions of theoptical spectrum when illuminated with said ultraviolet light, and (B) asecond portion comprising second detail elements complementary to saidfirst detail elements, said first and second portions being overlaidrelative to each other so as to complete said selected indicia.
 24. Anauthenticatable document as in claim 23, wherein said predeterminedcharacteristics of said authenticatable document are encodedsteganographically.
 25. An authenticatable document for identificationor for use in financial transactions, comprising: a) a substratesuitable for printing with fluorescent ink, and b) selected indicia,selected portions of said selected indicia being printed on saiddocument with fluorescent ink containing predetermined concentrations ofone or more fluorescent substances, both said selected indicia and saidfluorescent substances encoding predetermined characteristics of saidauthenticatable document, said selected indicia being selected frompredetermined sets of graphic images recognizable by automatic imagecomparison only when said selected portions of said selected indicia areilluminated with ultraviolet light, said selected indicia being furthercharacterized in that each of said selected indicia comprises twoportions in complementary pair relationship, neither of said twoportions by itself forming a complete recognizable image: (A) a firstportion comprising first detail elements that emit fluorescent light inpredetermined portions of the optical spectrum when illuminated withsaid ultraviolet light, and (B) a second portion comprising seconddetail elements complementary to said first detail elements, said firstand second portions being overlaid relative to each other so as tocomplete said selected indicia.
 26. An authenticatable document foridentification or for use in financial transactions, comprising: a) asubstrate suitable for printing with ink visible only under illuminationwith light outside of the visible spectrum, and b) selected indicia,selected portions of said selected indicia being printed on saiddocument with said ink visible only under illumination with lightoutside of the visible spectrum, said selected indicia being furthercharacterized in that each of said selected indicia comprises twoportions in complementary pair relationship, neither of said twoportions by itself forming a complete recognizable image: (A) a firstportion comprising first detail elements that emit fluorescent light inpredetermined portions of the optical spectrum when illuminated withsaid light outside of the visible spectrum, and (B) a second portioncomprising second detail elements complementary to said first detailelements, said first and second portions being overlaid relative to eachother so as to complete said selected indicia, and both said selectedindicia and said ink encoding predetermined characteristics of saidauthenticatable document, said selected indicia being selected frompredetermined sets of characters readable by automatic optical characterrecognition only when said selected portions of said selected indiciaare illuminated with light outside of the visible spectrum.